Pharmacokinetics and brain distribution of unbound levamisole in the anesthetized rats using microdialysis and microbore column liquid chromatography

A sensitive microbore liquid chromatographic method was developed for analysis of protein-unbound levamisole in blood and brain of anesthetized rats. Microdialysis probes were simultaneously inserted into the jugular vein toward right atrium and the striatum of brain of the male anesthetized Sprague–Dawley rats for biological fluid sampling after the administration of levamisole (3 mg/kg, i.v.) through the femoral vein. Assay of unbound levamisole was carried out using a microbore Phenyl-Hexyl column (150 mm × 1 mm i.d.; particle size 5 μm). The mobile phase consisted of methanol–10 mM 1-octanesulfonic acid which was adjusted to pH 3.0 with orthophosphoric acid (52:48, v/v) and the flow-rate is 0.05 ml/min. The assay was performed by monitoring the wavelength of maximum UV absorbance at 213 nm. The retention time of levamisole in rat blood and brain dialysates were found to be 10.5 min. The present assay enhanced the detection sensitivity and enabled the determination of levamisole at 50 ng/ml. Average in vivo recoveries of blood and brain dialysate were 46 ± 4 and 12 ± 4%, respectively, at concentration of 1, 5, 10 μg/ml. The result indicates that this method was suitable to investigate the disposition of levamisole and its penetration into blood–brain barrier (BBB).